1. Field of the Invention
The present invention relates to a multichamber type muffler structure having a subassembly formed by fixing an inner cylinder and a separator and an outer cylinder formed by first wrapping a sheet metal around the subassembly and next welding an overlapping portion of the sheet metal.
2. Description of Background Art
In a conventional multichamber type muffler for a vehicle, an inner cylinder and a separator connected to an exhaust pipe or the like are supported in an outer cylinder so as to be movable in the axial direction of the outer cylinder. More specifically, the inner cylinder and the separator are not welded to the outer cylinder, in order to absorb a difference in the amount of extension between the outer cylinder and the inner cylinder. See, for example, Japanese Patent Laid-open No. 2007-23866. In this muffler, the outer cylinder is formed by first bending a piece of sheet metal into a cylindrical shape and next welding an overlapping portion near the opposite ends of the sheet metal. On the other hand, the inner cylinder and the separator are assembled to preliminarily form a subassembly. The subassembly is inserted into the outer cylinder, thus fabricating the muffler. However, it is difficult to remove welding residue on the inner surface of the outer cylinder prior to inserting the subassembly into the outer cylinder.
In another conventional multichamber type muffler for a vehicle, a separator and a pipe are assembled to form a subassembly, and an outer cylinder is formed by first wrapping a sheet metal around this subassembly and next welding an overlapping portion of the sheet metal. See, for example, Japanese Patent Laid-open No. Hei 11-207425.
In a muffler structure having an inner cylinder, an outer cylinder, and a separator having an outer diameter substantially equal to the inner diameter of the outer cylinder, wherein the inner cylinder and the separator are assembled to form a subassembly and the outer cylinder is formed by first wrapping a piece of sheet metal around the subassembly and next welding an overlapping portion of the sheet metal, there arises a problem such that the outer cylinder may be welded to the outer circumferential portion of the separator by welding the overlapping portion of the sheet metal. Accordingly, the separator cannot be moved in the outer cylinder in the case wherein a thermal expansion occurs in the muffler.